Pond Fish Care in Winter

Winter isn't the most exciting time of the year to be a water gardener, but it's one of the most important times for maintenance. Starting in the fall, water quality is a major focus to minimize debris and lower nutrient loads to prepare for winter shutdown. Fish that live in shallower ponds will need to relocate indoors until the spring. In a deep enough pond, fish are able to spend the winter at the bottom of the pond until the water warms up in the spring. Learn more about how to take care of your pond fish during the winter. 

What are my fish up to?

Fish are cold-blooded creatures; they do not generate their own body heat. As the water temperature drops, fish's metabolisms and bodies begin to slow down. They require less food and become sluggish. Once the water temperature drops below 50°F, their bodily functions nearly stop completely, similar to hibernation. They use any excess fat on their bodies for energy and swim to the bottom of the pond and hang out with their friends. The water in the deepest of the pond is actually the warmest; this is where the fish will hang out until spring.

Overwintering

The pond needs to be deep enough that the water will not freeze all of the way through. The fish need enough space to swim at the bottom of the pond without being too crowded. Typically, ponds that are at least 18 inches deep will have enough space for fish to overwinter unless you live somewhere with extreme winters. 

If your pond is too shallow, you can move the fish inside for the winter. The fish should be kept in a climate-controlled area. There will typically be less water in the temporary home than in the pond, and the fish are at risk of freezing. The holding container should be large enough to keep the fish from being too crowded. If the container is shallow, you can use pond netting to prevent the fish from jumping out. The fish will need oxygenation, either an aerator or a pump.

Fish Feeding

You'll need to feed your fish less once the weather consistently drops to the 60s and 70s in the fall. Their digestive tracts start to slow with the dropping temperatures. When the water temperature falls below 50 degrees, their systems come nearly to a halt and should not be fed at all. Their bodies cannot digest the food, and they can become sick. The uneaten food can also cause poor water quality. This pond fish feeding guide will give you step-by-step directions on how to feed your fish in all temperatures.

Overcooling

Pumps, fountains, and waterfalls can also cause overcooling. The surface water of the pond is the coldest during the winter, and the deepest sections in the bottom have the warmest water. Pumps, fountains, and waterfalls can cause this water to mix, quickly dropping the overall pond temperature and causing overcooling. The fish can become stressed or even harmed. That is why removing, cleaning, and maintaining pumps, fountains, and waterfalls is best once the water begins to freeze.

Surface Freezing

Once the temperatures drop enough, the pond's surface water freezes. If there are no openings in the surface ice, the water can not oxygenate. The fish still need sufficient oxygen levels despite being less active. The lack of oxygen is one of the main reasons for a winter fish kill.  

Aerators and de-icers are great for keeping a small portion of the surface unfrozen. Aerators should be placed in a shallow water area to prevent overcooling. Aerators diffuse oxygen directly into the water. As the bubbles rise to the surface, the water moves and agitates. The moving water keeps the surface from forming ice. 

Aerators may not work in severe winters and can be used along with a de-icer. De-icers use heat to melt an area of the surface ice. There is not enough heat to melt the entire surface or warm the water, but it is effective for keeping a small hole actively open.  

Tip: Do not use force if you need to quickly create an opening in the ice for pond maintenance. Using a drill, ice saw, or an ice pick to cut an opening into the ice creates shock waves that stress and can even kill the fish. Instead, you can use boiling water to create an opening in the ice without distressing the pond life.  

Water Quality

During the fall, keeping your pond as clean as possible is important. Debris that settles to the bottom of the pond during the fall begins to break down in the winter. Organic waste, like leaves, uneaten fish food, lawn clippings, etc., releases gases as they break down in the water. The frozen surface doesn't allow for natural oxygenation, so the gases have no place to escape. They become trapped and can be harmful to your fish. Before the surface freezes, remove any debris that falls into the pond water before it settles to the bottom and treat the pond with Sludge Remover. 

Things to watch out for:

Sick Fish

A fish's immune system also slows down during the winter, making them more vulnerable to parasites and diseases. Before closing your pond, check your fish for any signs of sores or parasites. Determine if the whole pond needs to be treated, or just a few fish. If the illness is isolated, the sick fish can be removed and treated in a separate container.  

Snow Fall

While falling snow is beautiful, it can be problematic for your pond. Snow buildup on the surface can prevent light from penetrating water. The pond plants produce oxygen and need light to photosynthesize. Removing snow also helps keep the pond visible so kids and wildlife don't accidentally fall into the water.

Predators

Fish are more vulnerable during the winter as they move more slowly. They cannot dart out of the way as they would in warm water. Fish also have less room to swim around and huddle together in warm water pockets, attracting predators. Structures like koi castle or pond netting can help protect fish. 

Power Outage

During a bad storm, the power may be affected. Power outages can last only a few hours or sometimes days. The aerator and de-icer won't be able to run without power, and the pond's surface will freeze over if given enough time. It may be unsafe to check on your pond during the storm and walk out to pour boiling water and create an opening. An uninterrupted power supply (UPS) or generator can give the pond power temporarily until the power comes back.

Pond fish care in the winter helps make the transition into spring easier. If your pond is deep enough, your fish will be safe spending the winter in the pond. They will be fairly inactive and go into a hibernation state but will be ready to start feeding and greeting you again when the weather warms up. Maintaining water quality is very important for fish and general pond health in spring. After a little help, your fish will be able to go back to their normal habits and schedule in the spring, ready for a new year of excitement and water gardening.